Level measurement systems

ABSTRACT

A density profiler for measuring a density profile of a medium including at least two liquids and gaseous phases includes an axially distributed source array providing at least 10 collimated ionising radiation beams; an axially distributed radiation detector array, each detector associated in use with one of the beams and producing an output signal in response to incident radiation; and an analysor for the detector output signals to determine the density of the medium traversed by the beams of radiation.

[0001] The present invention relates to a method and device forseparation of a fluid comprising several fluid components, especiallyseparation of a well fluid in connection with a pipe for production ofhydrocarbons/water.

[0002] It has previously be proposed that well fluids in vertical wellsshould be handled using separators. Such separators can comprisesemi-permeable filters which are only pervious to water as described inU.S. Pat. No. 4,241,787 or cyclones as described in NO 172426.

[0003] A disadvantage with these devices is that they are relativelycomplicated in their construction and/or have many moving parts.Moreover, the aforementioned solutions would require extensivemaintenance/inspection when used in wells having high pressure and hightemperature. Another factor is that these solutions are speciallyadapted for installation in vertical sections of wells. They would alsorepresent extra pressure loss and consume energy.

[0004] The above disadvantages can be avoided with the presentinvention. The invention has been specially developed to be able toseparate fluids in horizontal sections of wells, something which is veryadvantageous in the recovery of horizontal formations where the well isformed by means of horizontal drilling for example.

[0005] Other advantages to be achieved when using the invention inconnection with long (horizontal) wells in particular are:

[0006] less pressure loss owing to reduced transport of water togetherwith hydrocarbons

[0007] simpler (and smaller) downstream equipment for separation

[0008] the amount of water with chemicals released at sea can be greatlyreduced

[0009] no salt deposition in production equipment downstream of the well

[0010] minimisation of hydrates problem

[0011] minimisation of corrosion problems in transport pipes and processequipment (can lead to choice of cheaper materials

[0012] separation of oil/water in the well can lead to simplificationsowing to large drops, lack of stabilising surfactants, high temperatureand low viscosity

[0013] good capacity in relation to energy consumption and investments

[0014] In the following the invention will be described further by meansof examples and figures in which:

[0015]FIG. 1 shows an oil/water flow pattern diagram

[0016]FIG. 2 shows separation in a well separator as a function ofseparator length, (%) content of water in the product oil

[0017]FIG. 3 shows separation in a well separator as a function ofseparator length, (ppm) content of oil in the product water

[0018]FIG. 4 shows a well with production equipment and a separator

[0019]FIG. 5 shows an embodiment of a separator

[0020]FIG. 6 shows a second embodiment of a separator

[0021]FIG. 7 shows a flow diagram for a separator of the type shown inFIG. 6

[0022]FIG. 8 a),b),c) shows a third embodiment of a separator withdifferent flow patterns.

[0023]FIG. 9 shows a fourth embodiment of a separator.

[0024]FIG. 1 is a diagram which shows the flow in a fluid comprising anoil component and a water component in relation to the speed of theindividual component. As the figure shows it has been established bymeans of experiments that it is possible to achieve a stratified flow ifthe speed of flow of the components is of an order of magnitude of lessthan 0.6 metres per second.

[0025]FIG. 2 is a diagram which shows the results arrived at inexperiments carried out in a test rig using a light crude oil qualityfrom a field in the North Sea. The fluid essentially consisted of thefluid components oil and water. A dispersed flow with a speed of V_(mix)0.6 m/s was initiated in the rig. The tests were carried out to find outwhat criteria have to be satisfied to achieve the desired degree ofseparation. Other parameters were as follows:

[0026] System pressure 105 bar

[0027] System temperature 70° C.

[0028] Oil viscosity: 1.02 mPa*S

[0029] Oil density: 736 kg/m³

[0030] A separator consisting of a horizontal pipe with an insidediameter of D=0.78 m was installed in the rig.

[0031] The x-axis in the diagram is represented by a parameter asfollows:

60.3*(D ³ /Q)*L

[0032] where:

[0033] D=inside diameter of the separator pipe (metres)

[0034] Q=total volume flow of the well fluid (cubic metres/hour)

[0035] L=length of separator pipe

[0036] The above parameters include the total retention time for thefluid and a correction factor for varying head (sedimentation distance)at a constant retention time for the fluid, depending on differentvalues for the inside diameter of the pipe.

[0037] The y-axis of the diagram indicates the percentage quantity ofwater in the oil phase.

[0038] The diagram in FIG. 3 was produced by means of the experimentdescribed above. The y-axis of this diagram indicates the quantity ofoil in the water phase in parts per million (ppm), while the x-axis isthe same as in FIG. 2.

[0039] It should be noted that the results set out in the diagrams inFIGS. 2 and 3 are based on experiments carried out using a specific wellfluid and basically only apply to that fluid. Other well fluids wouldhave similar separation properties, however, which could therefore bedetermined by means of similar experiments. As well fluids can havedifferent emulsion stability properties, they would require a shorter orlonger retention time in the separator until equivalent separation wasachieved.

[0040] Based on the above experiments it is now possible to separate awell fluid in horizontal wells or wells with horizontal sections ofsufficient length. When a well fluid flows from a reservoir and inthrough perforations in a pipe in a well, the well fluid will assume adispersed flow. Downstream in the production pipe, particularly insections which are essentially horizontal, the fluid components canassume a stratified flow if the speed of flow of the well fluid is lowenough and the retention time is long enough. In the following practicalsolutions will be described for separation of such a flow based on theabove knowledge.

[0041]FIG. 4 shows the principal elements in a supplementary solutionfor recovery of a formation 2. A pipe is placed in a horizontal sectionof a well in the formation 2. The pipe 1 comprises a horizontaltransport pipe or separation 3 in which there is a separator 6. Upstreamof the separator the pipe 1 is attached to drainage elements orperforations 7 which permit well fluid to flow in. Downstream of theseparator the pipe 1 comprises a vertical riser 4. The pipe 1 can alsobe attached to a water injection pipe 5 with injection apertures 8 forinjection of separated water into the formation.

[0042]FIG. 5 shows an enlarged/detailed section of a supplementarysolution as illustrated in FIG. 4. At its upstream end the horizontaltransport pipe 3 is attached to an extension pipe 10 with perforations 7for drainage of the formation 2. Well fluid is fed into the extensionpipe 10 and flows in the direction of the separator. The extension pipecan be surrounded by a casing 11 in such a way that an annulus 12 isformed between these pipes. The annulus is closed off towards theseparator 6 by means of a packing 13 and if necessary cement. Ifnecessary the extension pipe 10 can be replaced with any type ofsupplementary solution over one or more reservoir sections.

[0043] The separator as illustrated in this example is a pipe-shapedbody or section of pipe 14 which has one or more drainage apertures 15at its downstream end to allow water to drain out of the separator 6.The drainage apertures are chiefly positioned in the bottom part of thesection of pipe 14. The pipe-shaped body can with advantage besurrounded by the casing 11 so that water which drains out of thesection of pipe 14 through the aperture(s) 15 will be collected in anannulus (16) formed between the section of pipe 14 and the casing 11. Ifnecessary the drainage apertures 15 can be adjustable by means of one ormore movable sleeves (17) which can cover/uncover the apertures. Thesleeves can be positioned inside the pipe 15 or surround it as shown inthe figure. The section of pipe 14 can with advantage be an extension ofa production pipe 22.

[0044] The annulus can be closed off with a packing 26 in the downstreamdirection and connected to a water injection pipe 5 for returning waterto the formation 2. If necessary the injection pipe can be connected toequipment such as a valve 30, pumps etc. (not shown) so as to achieve acontrolled return of water to the reservoir. If desirable the waterinjection pipe can be connected via a pipe 34 to equipment 31 such as acyclone for further separation of the water flow. The separated watercan then be fed back to the reservoir via a pipe 32 with injectionapertures 35, while oil containing water is fed back to the productionpipe 22 via pipe 33.

[0045] Alternatively the packing 36 can comprise a valve 27 which can beopened and which permits water to be fed to the surface via the annulus16 between the production pipe and the casing. If necessary just a smallflow of water can be fed up to the surface in this way, or by using aseparate pipe (not shown), for sampling and measuring the oil content ofthe water.

[0046] At its downstream end the separator 6 comprises a blocking device18 which closes off the cross-section of the section of pipe 14 with theexception of one or more apertures 19 in the top of the blocking device.The aperture(s) 19 permit(s) oil to flow from the separator to theproduction pipe 22. Upstream of the blocking device there is a gammadensiometer 20 which comprises sensors connected to a signal-processingunit (not shown) which makes it possible to establish the level of theboundary layer (level in vertical direction) between the fluidcomponents. This type of multilevel gamma radiation can be used to bothdetect the level and measure the concentration profile. Moreover, thephase boundary can be established and the oil in the water and water inthe oil determined. This type of registration system representstechnology of which the specialist is master and will therefore not bedescribed in detail here.

[0047] Depending on the purity of the water to be separated out from thewell fluid, the boundary layer 25 is regulated high enough in the pipe14 for a small percentage of water to be fed into the production pipe 22together with the oil if necessary. Regulation of the boundary layer,including achievement of a constant boundary layer at the desired placein the separator, can be carried out by controlling the outflows fromthe separator. This can for example be achieved by means of a valve 28in the production pipe or at the wellhead (not shown) which controls theamount of fluid taken out through the production pipe 22 and regulationof the amount of drained water using the sleeve(s) 17 and/or valve 30 inthe water injection pipe 5. The level of the boundary layer cantherefore be raised or lowered in the section of pipe 14 by means ofreciprocal regulation of the quantity of separated fluids. It should beunderstood that this regulation can be carried out using adata-processing unit (not shown) which processes the signals registeredby the gamma densiometer, processes them in accordance with a setprocedure or software and passes signals to admission devices (notshown) which are connected to the aforementioned valves for regulationof the separated fluids. This represents technology of which thespecialist is master and will therefore neither not be described indetail here.

[0048] Another system for regulating the vertical level of the interface25 between the fluid components is to measure the quantity of water inthe oil (WiO) and the oil flow (Q oil). These quantities are measureddownstream of the separator and can with advantage take the form ofcontinuous measurements. The measuring equipment can either be locateddown in the well, on a platform or on the surface. Using thisinformation the water in the oil can be plotted as a function of oilflow. As long as the oil/water boundary layer in the separator is lowerthat the oil outlet, the gradient of water in the oil in relation to theoil flow will be low. If the boundary layer approaches the oil outlet,the water in the oil will rise sharply as the oil flow increases. Thisinformation can easily be used to control the oil flow in such a waythat the separator just barely allows water into the oil outlet.

[0049] Alternatively the oil in the water (OiW) can be registered andused to control the level of the boundary layer. This registration canbe done at the surface by a small sub-flow of the water which isseparated in the separator being taken up to the surface foranalysis/measurement of the oil content.

[0050] If the speed of the well fluid is too high before it enters theseparator, with the result that the conditions for separation cannot beachieved, the speed can be reduced in several ways. The speed of thewell fluid upstream of the separator can for example be reduced bydecreasing the amount of the fluids extracted at the wellhead andinjection pipe.

[0051] Alternatively the speed of the well fluid can be regulated bylimiting the inflow through the drainage elements or perforations. Thiscan for example be done by closing off the perforations completely orpartly using one or more movable sleeves (23). Another method can be toinstall one or more restrictions in the extension pipe 10 or in anothersuitable place upstream of the separator. The restriction(s) will helpto limit the speed of the well fluid before it reaches the separator.Such restrictions can be bodies which are inserted in the pipe andexhibit a reduction in flow area. Disc-shaped restrictions (plug withpassage for fluid) can be used for example.

[0052]FIG. 6 relates to another embodiment of a separator 106 and showsa detailed cross-section through a separator in a supplementary systemas shown in FIG. 4. As in the previous example the horizontal transportpipe 103 is connected at its upstream end to an extension pipe 110 withperforations 107 for draining the formation 102. Well fluid is fed intothe extension pipe 110 and flows in the direction of the separator 106.The extension pipe is surrounded by a casing 111 in such a way that anannulus 112 is formed between these pipes. The annulus is closed offtowards the separator 106 by means of a packing 113 and if necessarycement. In this embodiment the extension pipe is closed off at the inletend of the separator. The extension pipe 110 can if necessary bereplaced with any type of supplementary solution over one or morereservoir sections.

[0053] The separator as shown in this example is a pipe-shaped body orsection of pipe which represents an expansion in relation to the flowarea in the extension pipe 110. The section of pipe can with advantagebe the casing 111. If the diameter of the separator is expanded as shownin this embodiment, the length of the separator can be reduced.

[0054] At the outlet end of the separator there is a production pipe 122which is surrounded by the casing 111. The annulus 116 formed betweenthese pipes is sealed with a packing 118 which has one or more apertures119 in its bottom part to allow water from the separator to flowthrough. The water can follow the annulus between the production pipe122 and the casing 111 either to the surface or to a water injectionpipe 105. Oil is fed out of the separator by means of the productionpipe 122. The production pipe can project into the inside of theseparator with advantage.

[0055] It should be understood that the arrangement described under FIG.5 for regulation of the boundary layer between the fluid components andregulation of the speed of the well fluid can of course also beimplemented in this solution. The same applies to what was describedregarding the systems for injection and further separation of the watercomponent.

[0056]FIG. 7 shows a flow diagram for a separator 106 of the typeillustrated in FIG. 6, in which the dispersed oil/water flows into theseparator from an extension pipe 110. This example uses a 7″ extensionpipe and a 10¾″ casing 111 as the outer pipe of the separator. Theheight of the annulus is specified by the length H (distance betweenextension pipe and casing).

[0057] In this example there is at the distance 8H acoalescence-promoting insert or screen 140 which is a pierced disk witha cut in its bottom part. When the disc is inserted in the separator theaforementioned cut will form an aperture 141 which will permit theheaviest fluid components to flow through. The separator can compriseadditional screens 142, 143 inserted downstream of the first screen.Such inserts or screens can be used to promote separation in such a waythat the speed of the fluid to be separated can be increased in relationto what has been stated above. As the diagram shows, drops (oil) willcoalesce and float up in the top part of the separator. With a speed of0.9 m/s in the separated flow and a separator length of 26 m the flowwill be layered towards the separator outlet (production pipe inlet) insuch a way that the oil flows into the production pipe 122 and the waterenters the annulus 116. The other parameters for the flow illustrated inthe diagram are viscosity 2 cp, oil density 880 kg/m³, rate 4000 Sm³/d,water cut 30%.

[0058]FIG. 8a) relates to a third embodiment of a separator 206 andshows a detailed cross-section through a separator in 2 supplementarysystem as described in FIG. 4.

[0059] This embodiment has a number of structural similarities with thepreceding examples, but has a diameter which may be larger than thatpermitted by the diameter of the casing.

[0060] The horizontal transport pipe 203 comprises an extension pipe 210and a casing 211. Between these two pipes there is an annulus 212 whichcan if necessary be separated from the reservoir using a packing 226. Onthe upstream side of the separator there is a plug 213 which closes offthe extension pipe 210. If necessary a packing 225 can be fitted in theannulus 212 in such a way that it covers the entire area of the annuluswith the exception of one or more apertures 214 in the bottom part ofthe annulus for example. Upstream of the plug 213 the extension pipe hasone or more apertures 215 in its bottom part for example which permitwell fluid being transported in the extension pipe 210 to flow out intothe annulus 212. The fluid passes through the apertures 214 in thepacking 225 and the flows into the separator 206.

[0061] The separator as illustrated here is a radial expansion of theoutside dimension of the transport pipe 203, but as in the previousexample the outside dimension can if necessary be the same as theoutside dimension of the casing. The separator comprises an annulus 216formed between a perforated pipe 218 and a section of pipe 217 which canbe an expanded well hole supported by or closed off by means of anexpandable pipe, a material hardened in situ or a consolidated formation(not shown in detail). Such pipes can be installed in accordance withinherently known techniques. The perforated pipe 218 can be supported atits upstream end by the extension pipe 210 At its downstream end theperforated pipe is connected to a production pipe 222. Alternatively theextension pipe, perforated pipe ad production pipe can be a continuouspipe with the specified apertures 215. 221 and plug 213.

[0062] The annulus of the separator 216 is equipped to communicate withthe annulus 212 at its upstream end and with an annulus 223 formedbetween the production pipe 222 and the casing 211 at its downstreamend.

[0063] Well fluid which flows into the annulus 216 will be separated inthat fluid components with the lowest density (oil and possibly gas)will push up into the top part of the annulus. Here the perforated pipe218 is equipped with outlets or apertures 221 which allow the fluidcomponents to advance into the pipe and flow on downstream of theproduction pipe 222. Fluid components with a higher density such aswater will be collected in the bottom part of the annulus. The annuluscommunicates downstream with annulus 223 and the heavier fluidcomponents will therefore be carried away from the separator in thisannulus.

[0064] A packing 219 is fitted in the annulus 223 downstream of theseparator. The packing covers the entire area of the annulus with theexception of one or more apertures 224 in the bottom of the packing. Theapertures allow the heavier, separated fluid components to flow through.

[0065] It should be understood that the arrangement described under FIG.5 for regulation of the boundary layer between the fluid components andregulation of the speed of the well fluid can of course also beimplemented in this solution. The same applies to what was describedregarding the systems for injection and further separation of the watercomponent.

[0066] The apertures 221 in the perforated pipe 218 can with advantagebe designed with the regulation system which is to regulate the level ofthe boundary layer in mind, so that control of the outflows from theseparator are as even as possible. This can be achieved by the aperturesbeing slit-shaped in the vertical direction or triangular with onecorner pointing down (not shown) so that an increase in the level of theboundary layer 227 will produce a limited/progressive increase of waterin the oil which is taken out through the apertures 221.

[0067]FIG. 8b) shows the same solution as is shown in FIG. 8a), but withanother flow pattern where apertures 221 are provided on the lower sideor the pipe 218 such that the heaviest fluid components, i.e. the waterflows into the pipe and further up through the production pipe 222,while the lighter components flows up through the annulus 223.

[0068]FIG. 8c) shows a further flow pattern, where the pipe 218 isprovided with apertures on the upper as well as the lower side of thepipe, and whereby the lighter fluid components will flow into the pipeand into upper side, while the heavier components will enter into thepipe 218 at its lower side. For inside the pipe 218 is provided twoseparate pipes or channels 228,229 for further separate transport of thetwo respective fluid components.

[0069]FIG. 9 shows a fourth embodiment of a separator according to theinvention—moreover, FIG. 9a) shows a part of a well system 301 withdrainage pipe and branch pipes 302 and a separator 305 with a waterinjection well 304, FIG. 9b) shows in enlarged scale part of the wellshown in FIG. 9a), and FIG. 9c) shows a section along line A-A in FIG.9b).

[0070] As is shown in the figure, the separator includes a transportpipe 303 with a joint injection well pipe 304. Oil and/or gas mixed withwater flows via inflow restriction devices 316 from the drainage pipeand branch pipes 302 to the transport pipe 303 in the separator 305.Here the water and oil is separated with an upper 308 and lower 307layer respectively. Preferably, a threshold 315 may be provided in thearea where the transport pipe 303 and injection pipe 304 interconnect.Such threshold will secure water being present at a certain level.

[0071] The water flows further to the water injection pipe 304, whilethe oil flows upwards to the production pipe 306. The water flowing intothe water injection pipe 304, will contain oil which will be separatedin the upper part of the pipe (oil-/water interface at 309). A levelcontrol 310 (not further shown) detects the oil level and controls apump 311 which injects the water down into the injection pipe 304. Thelevel control may a capacity type or a combination of capacity andconductivity type control.

[0072] It should be emphasized that the drawings are just giving anindication of the different dimensions and distances being used inconnection with any practical solution of the invention. Thus, forinstance the distance between the transport pipe 303 and the control310, and the distance between the transport pipe and the pump may be of50 to 100 metres or more.

[0073] The pump 311 as shown in the figure is preferably provided at theend of a completion string 312, close below a packing 313 which separatethe separator 305 from the lower part of the injection well pipe. Thecompletion string contains (not shown) electric or hydraulic lines forthe supply of energy to the pump.

[0074] Besides, the completion string is provided with apertures 314 onthe upper side of the packing 313 so that the water being injected tothe injection well may flow through these apertures, further through thestring 312 and to the pump 311.

[0075] The invention is not limited to the above examples. Thus, it mayalso be relevant to use coalescence-promoting chemicals in connectionwith the separator. This may be relevant where surfactants are present(e.g. asphalt particles which cannot be held in solution by resins) andprevents drops joining. The effect of the surfactants can becounteracted by oil-soluble emulsion breakers/antifoam agents andasphalt dispersants. If necessary these can be injected continuouslyupstream of the separator.

[0076] It is also possible to connect additional valves to the inlet andoutlets of the separator to regulate the inflow of well fluid and theoutflow of the fluid components. The separator can also comprise otheravailable equipment for monitoring/checking that its operatingconditions are being met. It can for example comprise equipment formeasuring the volume flow/speed/pressure/temperature of the fluid/fluidcomponents.

1. Method for separation of a fluid comprising several fluid components,especially separation of a well fluid in connection with a pipe forproduction of hydrocarbons/water, characterised in that the fluid is fedinto one end of a mainly horizontal section of pipe or bore in which thefluid is set to flow at such a speed that the fluid is separated and aboundary layer is formed between the fluid components, whereby fluidcomponents with a low density are formed in the top part of the sectionof pipe and fluid components with a higher density are formed in thebottom part of the section of pipe, and that the fluid components aretaken out through separate outlets.
 2. Method according to claim 1 ,characterised in that the speed of the fluid to be separated isregulated by means of restrictions or the like placed upstream of thesection of pipe.
 3. Method according to claim 1 , characterised in thatthe speed of the fluid to be separated is regulated by means of flowregulation of the separated fluid components.
 4. Method according toclaim 1 , characterised in that the level of the boundary layer isdetected by means of measuring equipment and set by means of reciprocalflow regulation of the separated fluid components which are taken out ofthe section of pipe.
 5. Method according to claim 1 , characterised inthat the fluid components with the highest density are injected backinto the formation, if necessary after passing through a furtherseparation stage, with the fluid components with a lower density beingbrought up to the surface of the formation.
 6. Device for separation ofa fluid comprising several fluid components, especially separation of awell fluid in connection with a pipe for recovering hydrocarbons/water,characterised in that it comprises a mainly horizontal section of pipeor bore (14) with an inlet (10) for the fluid to be separated and atleast two outlets (15, 19) for the separated fluid components, with thelength of the pipe being such that the fluid is separated and a boundarylayer (25) is formed between the fluid components by the actualconditions of flow, whereby fluid components with a low density areformed in the top part of the pipe and fluid components with a higherdensity are formed in the bottom part of the pipe.
 7. Device accordingto claim 6 , characterised in that the horizontal section of pipe is anannulus (216) formed between an inner perforated pipe (218) and an outerpipe element (217) which can be an expanded well hole.
 8. Deviceaccording to claims 6-7, characterised in that the section of pipe (111,216) has a flow area which is greater than the flow area at its inlet(110, 212).
 9. Device according to claims 6-8, characterised in that thepipe has inside it one or more coalescence-promoting inserts, preferablyin the form of a pierced disc (140) with a downward-pointing cut (141).10. Device according to claims 6-9, characterised in that regulationdevices (30, 28) are fitted downstream of the outlets for the separatedfluid components for regulating the outflow of the individual fluidcomponents from the section of pipe.
 11. Device according to claim 10 ,characterised in that it comprises means (20) for detecting the level ofthe boundary layer (25), with the means for detection sending signals toa signal-processing unit which controls the regulation devices (30, 28)for the separated fluid components.